1. Field of the Invention
The invention relates to an exhaust gas purification device for internal combustion engines. Such devices are used especially with Diesel engines, emergency power generator installations, construction machinery and Diesel locomotives, where the emission of soot particles is subjected to after-burning, so that the quantity of emitted soot particles is drastically reduced.
2. The Prior Art
Such devices are methods for reducing the amount of soot particles with the help of exhaust gas after-treatment with ceramic filters are well-known in the state of the art. It is known, furthermore, to regenerate the filter material with the help of after-burning of the soot particles, whereby certain small amounts of a catalyzing additive are added to the fuel used. Such an additive produces an exothermic chemical reaction with the soot particles, so that the ignition temperature of the soot particles is practically lowered.
In the past, monolithic ceramic filters were found to have only little advantageous effect on the operating life of the filter, because the filters broke after a short time due to sudden overheating caused by thermal stresses.
So-called fabric filters, which basically consist of a great number of assembled ceramic filaments, appear to be far more favorable. Such type of filter is more elastic in its overall behavior and consequently capable of withstanding the possible occurrence of thermal stress in a superior way. The soot particles exiting from the engine are collected by a ceramic matting and, due to the reduction in the combustion temperature effected by the added additive, the regeneration process of the filter starts early at about 320.degree. C., a temperature practically reached on the filter shortly after the engine has been started. For regenerating the filter, thus no further measure or device is required for putting the ignition temperature into action. Additional filter regeneration devices are relatively expensive and, furthermore, require considerable expenditure with respect to energy to be supplied, which makes the overall installation uneconomical.
The ceramic filters known heretofore, which are woven or knittted using ceramic yarn, all have the decisive drawback that they are not capable of maintaining their initially adjusted material density in the hollow body of the filter while operating over longer periods of time, for the reason that they "collapse" within themselves. Attempts to provide the filter fabric with a certain amount of stability by inserting steel nettings in the fabric were only moderately successful because the useful life of the filters does not suffice for continuous operation.